The present invention relates to packaging comprising a piston, and a process for production of this packaging. This packaging contains in particular a liquid to be sprayed by means of a propulsive gas. This package can be used in the fields of foodstuffs, chemistry, cosmetics, dermatology, insecticides or cleaning agents.
It is known to use packaging of cylindrical shape, generally called an aerosol can, comprising internally a piston capable of sliding along a greater portion of the length of the packaging, generally the longitudinal axis.
The pistons of this packaging are conventionally provided with joints matching the shape of the packaging/piston assembly, such as for example a toric joint or O-ring. These joints ensure sealing of the piston and hence of the packaging relative to the liquid and the gas present in the compartments separated by the piston. This sealing being insufficient as to the liquid (the gas can pass into the liquid), it is moreover necessary to reinforce the seal by the presence of a sealing lip mounted on the joint secured to the piston. Thus, when the piston slides along the major axis of the packaging, the combination of the sealing lip and of the joint on the piston permits, whilst scraping the internal wall of the packaging, ensuring correct sealing of the packaging as to the liquid that it contains.
Unfortunately, the combination of these two elements does not permit sufficient sealing between the gas and the liquid present in the packaging. Thus, the gas under pressure diffuses slowly and constantly toward the liquid despite the combined presence of the joint and of the sealing lip of the piston. This slow and constant diffusion of the gas is due to the presence of a multitude of score lines parallel to the longitudinal axis of the packaging; the presence of these score lines is a result of the process of drawing used during production of the packaging.
One way to overcome this sealing problem consists particularly in cladding the internal wall of the packaging with a varnish. But no matter what the physical-chemical properties of this varnish, it is impossible completely to fill in the score lines.